The present invention relates to a communications system of the type including a central station and a plurality of substations. Such a communications system is disclosed, for example, in "Digitale Verfahren der Nachrichtentechnik" [Digital Communications Methods], Proceedings of the Conference of Professors, 1979, at the Fernmeldetechnisches Zentralamt, at pages 129-160. Reference to multiple utilization of the transmission band in connection with TDMA [Time Division Multiple Access] communications systems has already been made in the periodical "Frequenz" [Frequency], Volume 25, 1971, No. 10, pages 294-298.
In TDMA communications systems whose substations are connected together by way of a central station, the waiting times for frame establishment are fixed by the central station which informs the substations thereof. In the communications systems disclosed in "Digitale Verfahren . . . ", supra, the relatively long signal delay times between satellite and ground stations make multiple utilization of the transmission path, particularly two-way transmission in the same frequency band, somewhat inefficient with respect to the information density that can be processed.